# RD Sharma Solutions for Class 9 Maths Chapter 21: Surface Area and Volume of a Sphere

A Sphere is a geometrical 3-dimensional solid round structure obtained by the rotation of a semicircle along a diameter. There are several day-to-day objects which are spheres such as cricket ball, football, world globe, planets, marbles etc.

There are several properties and formulas which we will learn in this chapter. For example, the properties of a sphere are:

• If we rotate a semicircle is rotated about its diameter, then a Sphere is formed
• The sphere is not a polyhedron
• 4 non-coplanar points form a sphere
• If we cut a sphere into half about its centre, a hemisphere is formed.
• All the points on the surface of the sphere are equidistant from the centre of the sphere
• The circumference and the width of a sphere are always constant.
• It has a perfectly symmetrical structure
• The mean curvature of a sphere is always constant

The sphere has several formulas to determine its Surface Area and Volume of the sphere.

There is only one surface area of a sphere. The formula to determine its surface area is 4πR2 square units (where R = radius of the sphere), and the formula to calculate the volume of a sphere is 4πR3/3 cubic units (where R = radius of the sphere and π = 3.14)